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Fake modpost stage for LINUX_COMPILE.

Currently, when building a test case, we're compiling an entire Linux
module from beginning to end. This includes the MODPOST stage, which
generates a "conftest.mod.c" file with some boilerplate module
declaration code.

This poses a problem when configuring for built-in on kernels which have
loadable module support disabled. In this case conftest.mod.c is
referencing disabled code, resulting in a compilation failure, thus
breaking the tests.

This patch fixes the issue by faking the modpost stage when the
--enable-linux-builtin option is provided.  It does so by forcing the
modpost command to be /bin/true, and using an empty conftest.mod.c file.
The test module still compiles fine, although the result isn't loadable,
but we don't really care at this point.

Note it is important to preserve the modpost stage when building out of
and ZFS_AC_KERNEL_BLK_RQ_BYTES configure checks all depend on it to
identify GPL-only symbols.

Signed-off-by: Prakash Surya <>
Signed-off-by: Brian Behlendorf <>
Issue #851
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dechamps authored and behlendorf committed Jul 16, 2012
1 parent 319a99a commit fc88a6dda92a4fc00491a8afa24d144cc94063e4
Showing with 500 additions and 250 deletions.
  1. +4 −2 config/kernel.m4
  2. +496 −248 configure
@@ -444,10 +444,12 @@ dnl # ZFS_LINUX_COMPILE_IFELSE / like AC_COMPILE_IFELSE
dnl #
m4_ifvaln([$1], [ZFS_LINUX_CONFTEST([$1])])
- rm -Rf build && mkdir -p build
+ rm -Rf build && mkdir -p build && touch build/conftest.mod.c
echo "obj-m := conftest.o" >build/Makefile
+ modpost_flag=''
+ test "x$enable_linux_builtin" = xyes && modpost_flag='modpost=true' # fake modpost stage
- [AC_TRY_COMMAND(cp conftest.c build && make [$2] -C $LINUX_OBJ EXTRA_CFLAGS="-Werror-implicit-function-declaration $EXTRA_KCFLAGS" $ARCH_UM M=$PWD/build) >/dev/null && AC_TRY_COMMAND([$3])],
+ [AC_TRY_COMMAND(cp conftest.c build && make [$2] -C $LINUX_OBJ EXTRA_CFLAGS="-Werror-implicit-function-declaration $EXTRA_KCFLAGS" $ARCH_UM M=$PWD/build $modpost_flag) >/dev/null && AC_TRY_COMMAND([$3])],
[_AC_MSG_LOG_CONFTEST m4_ifvaln([$5],[$5])]
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